Head-up display (HUD) systems have been used in a variety of aircrafts, particularly associated with military applications for decades. Recently, more and more similar systems can be found in commercial automobiles. To be able to integrate the head-up display system into the console or the instrument panel of the automobiles, the bulky components of the system, such as the information display module, should be substituted with more compact units, e.g. a projection module, related to the head-up display system. Based on the above requirement, the projection module using laser light source is introduced into the head-up display system. The head-up display system receives the text or image information from the automobile and transfers it into the control signal of the laser light source. Then, the laser light source is projected onto a display medium in a scanning manner. The control signal manipulates the on/off sates of the laser, and thus the text or image information is re-generated in frames on this display medium. The driver in the automobile can see the information and make reactions accordingly.
Conventionally, the head-up display system employs a holographic element as a display medium. However, the holographic element has to be embedded into the windshield of the automobile. Manufacturing of such structure is quite complicated and thus increases the cost of the head-up display system. Moreover, the focal length of the virtual image located at one side of the holographic element is fixed. While the driver adjusts the seat height or angle, the distance from the driver's eyes to the windshield is changed. Once that distance is out of the focal length, the virtual image becomes blurred. The driver will be forced to move his (or her) head and body in order to get into focus. This may cause safety issues, especially when driving, and eventually nullify the head-up display system. Consequently, there is a need to develop a novel head-up display system to solve the above-mentioned problems.